Porcine intestinal adenomatosis is a form of ileitis that can cause chronic mild diarrhea and reduced performance in growing pigs.

Although ileitis was first identified in 1931, more than 70 years later, there still is no clear formula for controlling it in every swine production system, experts say.

To help control ileitis, some veterinarians and/or producers rely on feed-grade antibiotic programs, vaccine programs or on a combination of diet, antibiotics and vaccine.

“The real test for any ileitis control program is July through September,” stresses Tim Loula, swine veterinarian with Swine Vet Center, St. Peter, Minn. “We’ve come to recognize that while management factors may trigger an outbreak of ileitis in a group of pigs – the disease is also highly seasonal.” (See sidebar below.)

Current estimates place annual economic losses from ileitis at approximately $100 million per year for the U.S. swine industry. Information from the National Animal Health Monitoring System (NAHMS) in 1997 found that more than 96 percent of the swineherds in the United States were positive for ileitis.

What is known
Proliferative enteropathy (PE), more commonly known as ileitis, is divided into two clinical forms. Chronic mild diarrhea and reduced performance in growing pigs is known as porcine intestinal adenomatosis, while acute hemorrhagic diarrhea and sudden death of market age or replacement animals is known as proliferative hemorrhagic enteropathy. Both are caused by Lawsonia intracellularis, an obligately intracellular bacterium.

In addition to pigs, non-human primates, hamsters, rabbits, rats, mice, guinea pigs, foals, sheep, white-tailed deer, emu, ferrets, arctic foxes, dogs and certain birds play host to PE.


Minnesota swine veterinarian Tim Loula reports that the most difficult cases of ileitis seem to strike seasonally – in late summer usually from July through September.

The basic knowledge of ileitis has been obtained primarily through clinical observation. Because the disease is an obligate intracellular pathogen with limited reagents for study, in-depth research by traditional methods has not been productive, according to experts.

Ileitis spreads primarily through fecal-oral routes within a herd. According to  swine veterinarian John Deen, associate professor of veterinary medicine at the University of Minnesota, once pigs are infected, the organisms can be continuously shed for up to 10 weeks.

However, this does not necessary mean that sows will automatically pass the disease on to their piglets, according to Deen.

“Vertical transmission from sow to piglet has not been confirmed as a predominant means of transmission,” he points out. In fact, while sows seldom break with ileitis, they do provide piglets with passive immunity to the disease. Immunity from a natural outbreak of PE in sows and pigs ranges from four weeks to three months.


Vertical transmission of ileitis from sow to piglet has not been confirmed as a predominant means of transmitting the disease.

Research also shows that production systems may also play a role in the timing of infection. Pigs in a farrow-to-finish, continuous-flow system, for example, typically show seroconversion between 8 to 16 weeks. In a multiple site system, the seroconversion is more likely to occur between 16 to 20 weeks.

Being aware of one or more of the following symptoms in a herd can help you identify or rule out ileitis:

  • Initial infection often occurs in nursery pigs (less than 12 weeks of age) as proliferative lesions of the ileum/colon resulting in diarrhea and uneven weight gain.
  • The acute form is expressed as rapid onset of diffuse hemorrhagic lesions resulting in sudden death found primarily in grow-finish pigs and replacement gilts.
  • Transmitted predominantly through fecal-oral routes in pigs, although additional vectors might include mice, small birds and insects.

Many issues surrounding ileitis such as infection vectors, transmission and survivability remain unknown due to lack of adequate testing methods.

“The difficult nature of reproducing L. intracellularis in the lab is part of the problem,” states Deen. “The other side of the coin is complacency on the part of industry to really understand the disease when antibiotic and vaccine tools are working at an acceptable level for most swine producers.”


University of Minnesota swine veterinarian John Deen says that once pigs are infected with the ileitis-causing organism, the organism can be shed for up to 10 weeks.

However, diagnostic tools for seroconversion, strain variability and differentiation between live and dead bacteria are leading the way to a better understanding of ileitis and its causative agent, L. intracellularis.

“The ability to differentiate between live and dead bacteria through staining is one of the most exciting new tools we have for ileitis,” explains Deen. “This opens the door for us in determining longevity and survivability of the bacteria.” 

With the development of molecular genetic typing, researchers are able to distinguish the variation between strains of L. intracellularis. Using variable-number tandem repeat (VNTR) testing, University of Minnesota researchers have shown “that samples from epidemiologically unrelated PE herds and outbreaks had unique VNTR profiles.”

This same research estimates that the probability that two unique isolates will have identical profiles by chance is less than 1 in 313,600. However, research results also show that L. intracellularis isolates from the same outbreak shared identical VNTR profiles, suggesting that the bacteria remains stable for short periods of time within a swineherd.


Proliferative hemorrhagic enteropathy is another form of ileitis that can cause acute hemorrhagic diarrhea and sudden death in market age or replacement animals. Both forms are caused by Lawsonia intracellularis, an obligately intracellular bacterium.

Treatment options
Establishing an effective treatment program still is a challenge and can be a moving target for many swineherds.

“We see herds with a variety of symptoms ranging from looseness of stools in early grow-finish to acute outbreaks within three weeks of market to gilts on the sow farm experiencing acute hemorrhagic diarrhea and sudden death,” observes Loula. “We’ve yet to find a single treatment program that works for everyone,” he emphasizes.

For example, he adds, vaccine use is high in multiplier herds and replacement gilts. “Our recommendation is one dose in the nursery and one at selection for replacement gilts,” Loula says. Production and economic losses mount quickly if gilts break with ileitis and die when they enter the sow herd, he says.

Quite a few grow-finish operations have opted to rely more on feed-grade antibiotics to help control ileitis.

When ileitis breaks in a herd, immediate injection of clinically sick animals and all other like animals in the group is needed. “Our work also shows that Tylan or Lincomix in water medication is an effective treatment,” says Loula.

Water medication is more effective than feed medication because sick pigs tend to go off feed, and water is a fast way to treat a lot of pigs, Loula says.

“Widespread treatment is necessary because ileitis outbreaks can get very serious in a very short time,” stresses Loula. “You need to be treating the pigs that don’t look sick yet in order to prevent further problems. Recovery from the hemorr-hagic form of ileitis is poor, so you must prevent it.”

Editor’s note: The author is a Minnesota freelance writer who has written articles for Swine Practitioner magazine for several years.

Is ileitis a seasonal problem?

The ultimate test of an ileitis control program might just be its effectiveness without a recurring outbreak in late summer – July through September. “Our most difficult cases seem to strike during this time frame,” points out swine veterinarian Tim Loula, Swine Vet Center, St. Peter, Minn.


Loula attributes these summer outbreaks to several factors including:

  • Heat stress on pigs.
  • Poor feed quality due to the effects of heat and time on grain and fat components.
  • Feed consumption is interrupted or reduced by extreme heat.
  • Barns remain wet from higher humidity for longer periods of time providing an environment conducive to bacteria.

  “During the winter when ileitis outbreaks are less common, it’s easy to forget that it is the number one disease in grow-finish and gilt development operations in North America,” reminds Loula.